import java.util.*;

/**
 * @author LKQ
 * @date 2022/6/13 17:22
 * @description
 */
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextLine()) {
            String text = sc.nextLine();
            int[] cnt = new int[128];
            for (char c: text.toCharArray()) {
                cnt[c]++;
            }
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < 128; i++) {
                if (cnt[i] != 0) {
                    for (int j = 0; j < cnt[i]; j++) {
                        sb.append((char) i);
                    }
                }
            }
            System.out.println(sb);
        }
    }
}
